My glow plug light is not coming on and after doing some searching here I'm confused. I understand there is a glow plug strip fuse on the firewall right before the glowplugs but is there also a fuse somewhere that gives power to the Glow plug relay?


Car is a 1977 300D

Thanks,
Noah

A quick scan of my wiring diagram for that year does not easily reveal what I am looking for. Yet it is reasonable to assume the glow plug relay is fused additionally for the primary circuit in it as well.
Otherwise if the primary area of the relay developed a short an electrical fire might result. The large strip fuse is only for the secondary circuit. Sorry if this is not much help and I only responded as there were no other responses up till now.
If glow light still works you could pull one fuse at a time until you located it. It might be fuse #6. Additionally most cars have been pretty well almost totally fused since about the mid 1950s. Perhaps someone else with a better wiring diagram or experience with this circuit will post.
It might be better to post your actual problem if any as well. Those relays can develop some strange behaviours just as well as other components in that circuit.

Strange, but it does not look like there is a fuse on the "primary" side of the GP relay. It looks like the relay is energized when the key is on without any fuse in the circuit. Maybe I'm missing something on the wiring diagram.

I'm not familiar with your model and this is just a guess. When I looked up the relay in parts, there are 3 different versions. Which one do you have? On at least one, and possibly two, of the versions the fuse is a metal strip between two screws that is internal and is accessed by removing the relay cover.

Do you still have the series loop-style glow plugs? If one burns out, in that setup, the circut is open to power for all the rest.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

His car is a 1977 300d with the relay underneath the dash. I believe it has a separate secondary fuse.
The newer relay version that mounts under the hood on the inner fenderwell has the enclosed secondary fuse. I still figure the primary is fused well before the ignition switch. Of course I am not totally sure of that.
Manufacturers usually protect the dash area pretty well. I guess I had better go dig into that haynes wiring diagram a little further.